Percutaneous transluminal coronary angioplasty (PTCA) is used to increase the lumen diameter of a coronary artery partially or totally obstructed by a build-up of cholesterol fats or atherosclerotic plaque. Typically a first guidewire of about 0.038 inches in diameter is steered through the vascular system to the site of therapy. A guiding catheter, for example, can then be advanced over the first guidewire to a point just proximal of the stenosis. The first guidewire is then removed. A balloon catheter on a smaller 0.014 inch diameter second guidewire is advanced within the guiding catheter to a point just proximal of the stenosis. The second guidewire is advanced into the stenosis, followed by the balloon on the distal end of the catheter. The balloon is inflated causing the site of the stenosis to widen. The dilatation of the occlusion, however, can form flaps, fissures and dissections which threaten reclosure of the dilated vessel or even perforations in the vessel wall.
Although the dimensions in the above example are suited to the coronary arteries, any body lumen can be treated by percutaneous transluminal angioplasty (PTA), including the vas deferens, ducts of the gallbladder, prostate gland, trachea, bronchus and liver. The body lumens range in diameter from small coronary vessels of 3 mm or less to 28 mm in the aortic vessel. The invention applies to acute and chronic closure or reclosure of body lumens.
Soft distal segments are advantageous in guiding catheters for navigating tortuous paths in the vascular system. This has been achieved in the prior art by attaching discrete softer segments with varying durometer material to the distal end of a guiding catheter. As for example, commonly owned copending patent application for an Improved Method of Soft Tip Forming, U.S. Ser. No. 08/368/186 to Riopel and Horrigan as well as commonly owned copending patent application for a Guide Catheter with Soft Distal Segment, U.S. Ser. No. 08/543,992 to Brin et al. Discrete segments have the disadvantage of the possibility of joint separation. Joining multiple pieces requires more manufacturing time then would an extrusion. Buckling and kinking can also occur at joints where there is an abrupt transition in stiffness.
U.S. Pat. No. 4,904,431 to O'Maleki for "Process for Manufacturing Catheters" discloses a continuous extrusion of a first rigid polymer to form a cylindrical body which will define the inner rigid sheath of the catheter. A second soft, pliable polymer is then extruded over this cylindrical body to form an outer cylindrical layer, which will define the outer soft, pliable sheath of the catheter. Another embodiment involves reinforcing the cylindrical bodies with a stiffening material, typically a wire cord wrapped around the inner layer and embedded between the inner and outer sheaths of the catheter. The rigid polymer is extruded at a variable rate which is altered at prescribed locations to first successively diminish the thickness of the forming layer, and then successively increase the thickness, thus forming a depression. This location will form the tip region of two catheters. The overlaying of this location, during the second extrusion step, with the soft polymeric material will define the soft catheter tip. The final catheters are formed by cutting the resulting structure at the junction of where the thickness of the first forming layer begins to increase in thickness.
U.S. Pat. No. 5,533,985 to Wang for "Tubing" discloses in FIG. 10 "bump" tubing in which the insert end is of stiffer material and the bell end is of soft material.
What is needed is a means of attaching separate segments of catheter shaft to provide a soft distal segment on a high volume, low cost basis. It is an object of the invention to provide a continuous outer jacket, a continuous braided layer and a continuous liner throughout the length of the product resulting in greater safety while having a distal segment with a lower flexural modulus than the proximal segment. It is another object of the invention to improve kink resistance in the distal segment.